Google+ Badge


Saturday, March 6, 2010

I Attempt Feedback

As I mentioned in my last post, I'm working on a visual accompaniment to a piece of music, consisting entirely of images generated by video feedback. I've done this a couple of times before, but that was in the 1970's; since then I've played with feedback occasionally but not tried to do anything serious with it. The simplest form of video feedback involves pointing a camera at a screen displaying the output of the camera. Because there is a one-frame delay from when a pixel on the screen changes until that change is sent back to the screen from the camera, a delayed feedback loop is created. Here's a still photo taken off a video of the basic setup:

Now you can move, tilt, and zoom the camera to make some more interesting patterns:

Note the camera control icons in these stills. I don't have a video camcorder, so I tried to use the video mode of a point and shoot digital camera. In fact, I tried 2 different cameras, and found that I couldn't get rid of all the icons on either of them. My current budget is constrained enough that I can't afford to go out and buy a camcorder just now, so simple video feedback is problematic for this project.

Never fear, the computer will save me. Turns out it's not at all difficult to simulate video feedback with a program. On Mac OS X, there is a program called Quartz Composer that allows you to program complicated video effects in the Core Image API. You can build components (called "patches") for these programs using standard Mac Objective-C coding, but once they're built, you can wire them together with composer in a visual editor paradigm. Since the system comes supplied with a wide-range of patches, and there are more at various developer sites on the web, you can do a lot without ever writing any code. I made some simple feedback videos using input from the iSight camera in my laptop feeding into Quartz Composer; here's one still:

Here's a screen-shot of a composer editor window:

That window shows the wiring diagram for a feedback video that looks like this:

And here's a short video of another simulated feedback program:

I'm now working on the problem of getting the clips of simulated feedback into my movie editing software so I can cut them to the music. For some reason one of them worked, but the second one I tried can't be imported correctly. Oh, the joys of software! I'll post more on this subject as I make progress.


Tim Walters said...

Looks good! The audio feedback was all done digitally as well, so I think this method is very appropriate.

Tim Walters said...

Looks good! The audio feedback was done digitally as well, so this technique is perfectly appropriate.